Climate Change Impacts on Urban Sanitation: A Systematic Review and Failure Mode Analysis

Climate change will stress urban sanitation systems. Although urban sanitation uses various infrastructure types and service systems, current research appears skewed toward a small subset of cases. We conducted a systematic literature review to critically appraise the evidence for climate change impacts on all urban sanitation system types. We included road-based transport networks, an essential part of fecal sludge management systems. We combined the evidence on climate change impacts with the existing knowledge about modes of urban sanitation failures. We found a predominance of studies that assess climate impacts on centralized sewerage in high-income contexts. The implications of climate change for urban nonsewered and complex, fragmented, and (partially) decentralized sanitation systems remain under-researched. In addition, the understanding of the impacts of climate change on urban sanitation systems fails to take a comprehensive citywide perspective considering interdependencies with other sectors and combinations of climate effects. We conclude that the evidence for climate change impacts on urban sanitation systems is weak. To date, research neither adequately represents the variety of urban sanitation infrastructure and service systems nor reflects the operational and management challenges of already stressed systems.


Outcomes
Direct positive and negative climate-related impacts on urban sanitation systems that affect the delivery of safely managed sanitation.
Negative impacts include: damage on sanitation infrastructure (e.g., blockage or corrosion of pipes), disruption of services (e.g., inaccessible roads for emptying trucks, failure of sewer pumps and treatment processes due to electricity outages) and inhibited efficacy of the system (reduced efficacy of biological wastewater treatment processes, excessive leakage) Positive impacts include: prolonged life or reduced maintenance requirements of infrastructure (e.g., slower filling up of pit latrines), improved service delivery (less disruption of emptying services), improvement in system performance (e.g., improved efficiency in treatment processes) Positive or negative secondary impacts on human and environmental health and the economy (e.g., increased household or public expenditure on repairs or preventive maintenance, increase in specific waterborne diseases (e.g., cholera) after extreme weather events, increased business opportunities for emptying businesses, fish mortality or reduced biodiversity in receiving water bodies) Positive or negative non-economic secondary impacts (e.g., loss of privacy through the collapse of latrine superstructures, increased absenteeism due to the damage of school toilets)

Study types and designs
Qualitative and quantitative studies that assess or report on specific climate change impacts on urban sanitation systems Studies that do not specify climate change impacts.
Studies that exclusively refer to the impacts from a different study (e.g., to test adaptation measures). Studies that exclusively refer to non-climatic impacts on sanitation systems (e.g., urbanisation impacts)

Topic Criteria Questions
Notes on scoring (out of 1)

Objectives
Were the objectives and purpose of the study described?
0 if neither item below is included, 0.5 if one is included, and 1 if both items are included  overall purpose  objectives 2. Context Was sufficient detail provided on the context and setting of the study? 0 if neither item below is included, 0.5 if one is included, and 1 if both items are included  description of sanitation system (e.g., technologies, components, services, technical status of infrastructure)  details of climate change projection or extreme weather event 3. Data collection Was sufficient detail provided the data collection method and procedures? 0 if no information, 0.5 if partial detail is provided, and 1 if sufficient detail is provided.

Analysis
Was sufficient detail provided on analytical methods used in the study? 0 if no information, 0.5 if partial detail is provided, and 1 if sufficient detail is provided.

Interpretation
Is there a discussion and interpretation of the main findings?
0 if no information, 0.5 if discussion and interpretation is incomplete, and 1 if a complete discussion and interpretation is provided. 6. Limitations Were study limitations described?
0 if no information, 0.5 if limitations are incomplete, and 1 if full limitations are described. Quality of reporting

Conclusions
Were stated conclusions and implications within the scope of the study design and grounded in the data presented?
0 if conclusions are not stated or beyond the scope, 0.5 if partly beyond the scope, and 1 if conclusions are within the scope of the study.

Strength of evidence based on study method
How can the provided evidence presented in the results be classified? 0 if expert consultation, 0.5 if reported or modelled evidence, and 1 if empirical evidence. 9. Spatial scale and generalisability of impacts on sanitation system What is the spatial scale and generalisability of the presented evidence? 0 if study was very context specific with limited generalisability (e.g., impacts on sanitation system were dependent on specific project/interventions design), 0.5 if study was context specific (in terms of climate impacts and sanitation systems) but results that are transferable to similar contexts, and 1 if study had global scale or case independent approach.

Temporal scale and generalisability of climate effect
What is the temporals scale and generalisability of the studied climate effect? 0 if study presented evidence linked to a single occurrence of an extreme weather event, 0.5 if study presented evidence linked to multiple occurrences of similar extreme weather events, and 1 if study presented impacts linked to a longterm observation or (projected) climate change trend.
Highincome 0.  For the 2080s the simulation showed an increase for all three parameters under the high emissions scenario (up to 37% in total spill volume, 32% in total spill duration and 12% in spill frequency under the HadCM3 model). Under the B1 low emission scenario the system was expected to cope with CC impacts and a reduction in spill volume, frequency and duration was projected. Projected decrease of rainfall during the summer (bathing season) led to reduction of spill volume during that season but lower water levels and dilution in receiving waters could still pose a pollution threat. 7 5 Abdulla, F. and S. Farahat (6)

Primarily engineering
Qualitative -Reported evidence (experience from WWTP staff with land subsidence was used as proxy for future SLR) Japan/Tohoku region Risk of seawater intrusion into discharge pipe was reported. Ability to discharge treated wastewater by gravity would be dependent on level SLR and tidal cycle. Saltwater intrusion into treatment system were reported as concern as pump motors and aeration tanks were not designed to cope with high-salinity water. Rising groundwater (GW) levels lead to increased infiltration into sewer system and therefore reduced capacity of plants and exacerbated pipe corrosion.  70 Bíl, M., R. Vodák, J.
Kubeček, M. Bílová and J. Sedoník (61) Increase in rainfall Rapid snow melt Road network performance on various roads in Czech Republic Quantitative Empirical/reported data Czech Republic/various Authors investigated six major natural disasters which were all induced by extreme rainfall or by rapid snowmelt and resulted in floods and landslides. Impacts were evaluated with respect to damage to road networks and decreased serviceability. During one of the events the road network serviceability was reduced by up to 30% and the ratio of network lengths was reduced to 78.4% 7 71 Bilodeau, J.P., F.P. Drolet, G.  (83) observed that congestion did not evolve proportionally with reduction of traffic capacity and knock-on effects on traffic systems may be revealed delayed. Locations of traffic disruption could not be directly associated with areas of closed streets which showed that congestion can be related to lost connectivity far from flooded areas. 93 Qiao, Y., J. Santos, A.M.K. Stoner  Overflow of septic tanks Open defecation as coping mechanism with flooded toilets Poorly designed sewerage systems get blocked during rainfall 33 Howard, G. and J.
Bartram (97) Increased and more intense rainfall Decreased rainfall and more frequent occurrence of drought